To investigate the relationship between thigh muscle flexibility and anterior knee pain in adolescent athletes, we examined 46 skaters. We taught them flexibility exercises and later retested 28 of them. Three fourths of the skaters who improved their quadriceps flexibility eliminated their pain. Two of the three skaters who lost flexibility developed pain. Analysis of all examinations showed that skaters with pain had tighter quadriceps muscles than those without pain. Poor hamstring flexibility was correlated with patellofemoral pain. This study shows that adolescent athletes may improve their flexibility after counseling and indicates a clear relationship between thigh muscle flexibility and anterior knee pain.